The quality of a patient's life may be an indication of the severity or progression of a symptom or aliment, and also of the efficacy of a therapy to treat the symptom or ailment. For example, quality of life is directly related to the level of pain a patient experiences in everyday life. Accordingly, the quality of the patient's life may indicate the severity of the pain and effectiveness of therapies to treat the pain. The quality of a patient's life may similarly be impacted by: movement disorders, such as tremor, Parkinson's disease, spasticity, and multiple sclerosis; psychological disorders, such as depression, mania, bipolar disorder, or obsessive-compulsive disorder; cardiac disorders, such as congestive heart failure or arrhythmia; gastric disorders, such as gastroparesis; or obesity.
The quality of sleep experienced by a patient, the overall activity level of a patient, or the amount of time a patient spends engaged in particular activities, in particular postures, or above particular activity levels may indicate the quality of the patient's life, and thereby the effectiveness of a therapy used to treat a symptom or disorder, such as those identified above. However, such life quality metrics are not typically quantified for evaluation of disease state or therapy. For example, a major limitation of most of the pain literature is the poor assessment of sleep conducted in many studies. There are relatively few objective polysomnographic and actigraphic assessments, and most studies rely solely on retrospective subjective self-report measures of sleep disturbance.
Chronic pain may cause a patient to avoid particular activities, or activity in general, where such activities increase the pain experienced by the patient. When a patient is inactive, he or she may be more likely to be recumbent, i.e., lying down, or sitting, and may change postures less frequently. Additionally, sleep disturbance is perhaps one of the most prevalent complaints of patients with chronically painful conditions. Quality of sleep, quantity of sleep, and trouble falling asleep may be related to the intensity and frequency of pain.
Similarly, the difficulty walking or otherwise moving experienced by patients with movement disorders may cause such patients to avoid particular activities or posture, or movement in general, to the extent possible. Further, the uncontrolled movements associated with such movement disorders may cause a patient to have difficulty falling asleep, disturb the patient's sleep, or cause the patient to have difficulty achieving deeper sleep states. Additionally, many psychological disorders disturb a patient's sleep, and cause them to engage in less activity during the day. Patients with depression often spend much of the day in bed or otherwise recumbent.
Further, in some cases, poor sleep quality may increase the symptoms experienced by a patient due to an ailment. For example, poor sleep quality has been linked to increased pain symptoms in chronic pain patients, due to lowering the pain threshold of the patient. Poor sleep may similarly increase tremor in movement disorder patients or the level of symptoms for some psychological disorders. The link between poor sleep quality and increased symptoms is not limited to ailments that negatively impact sleep quality, such as those listed above. Nonetheless, the condition of a patient with such an ailment may progressively worsen when symptoms disturb sleep quality, which in turn increases the frequency and/or intensity of symptoms. The increased symptoms may, in turn, limit patient activity during the day, and further disturb sleep quality.